Some image readers (i.e., scanners) are made to move an optical unit that includes a light source, a photoelectric conversion device, and optical elements such as lenses and mirrors along a manuscript to form an optical path for guiding the reflected light from the manuscript to the photoelectric conversion device to obtain image data of the manuscript. The optical unit is integrated into a carriage, and a driving mechanism for moving the carriage, such as a driving or timing belt, is coupled with the carriage and is moved back and forth by rotation of a driving motor. A guide rod extends in the direction of the longer side of the carriage in order to guide the movement of the carriage.
The basic concept of attaching a mirror to a mount or carriage is disclosed in prior art patents, such as U.S. Pat. Nos. 3,918,806, 3,936,179 and 4,073,584.
Prior art FIGS. 7 and 8 show a traditional structure for attaching a mirror to an elongated carriage, with FIG. 7 being a vertical cross-sectional view and FIG. 8 being an exploded, oblique view. In the central section of the carriage 1, an elongated light source 2 is integrated in such a manner that the light source 2 illuminates a manuscript mounted on a platen glass 3 arranged above the carriage 1. The light from the light source 2 is condensed to a line above the upper surface.
An elongated strip-shaped, first mirror 4 is arranged in the vicinity of the light source 2 in order to receive light reflected from the manuscript. The first mirror 4 has a length that accepts light from the entire width of the manuscript. The light from the manuscript is incident onto the first mirror at angles which are substantially 45 degrees to the normal to the mirror 4 surface. Thus, the light after reflection from the mirror 4 travels substantially horizontally to a rod lens array 5 that is arranged at the front of the first mirror 4. The rod lens array 5 is formed of rod-shaped lenses arranged in parallel, wherein light rays reflected from the first mirror 4 enter a first end of the rod lenses, pass through the rod lenses, and exit after being appropriately converged.
An elongated second mirror 6 is provided at the second end of the rod lens array 5. The second mirror 6 is made in a strip shape and the reflection surface is inclined substantially 45 degrees to the horizontal so that the light rays traveling horizontally from the rod lens array 5 are reflected vertically downward. The photoelectric conversion device 7 is arranged underneath the second mirror 6. In the photoelectric conversion device, an appropriate number of photoelectric conversion units are arranged in parallel so that the reflected light rays from virtually the entire reflection surface of the second mirror 6 may be intercepted. The optical unit, including the light source 2, the first mirror 4, the rod lens array 5, the second mirror 6 and the photoelectric conversion device 7, is housed in a unit holder 1 a formed in an appropriate recessed area in the carriage 1. The photoelectric conversion device 7 is integrated in a sensor substrate 8.
In appropriate locations in the carriage 1, elongated reinforcement sheet metal members 9a and 9b are attached to increase the rigidity of the carriage 1. Covers 1b and 1c are placed over the carriage 1 that houses the optical unit. On both sides of the carriage 1 are attached covers 1e, 1e which interlock with a guide rod (not shown) that is provided in the casing of the carriage 1 in order to guide the movement of the carriage 1. A recessed area 1d is formed, as shown in FIG. 7, at one end of the carriage 1 in order to provide passage for an electrical harness 10.
In the conventional mirror attachment structure described above, the following problems may occur because the strip-shaped mirrors 4 and 6 are made to be attached on mirror table components 4a and 6a formed inside the unit holder 1a of the carriage 1, as seen in FIG. 7. Because the mirrors 4 and 6 are very thin, they must be handled with care, and careless handling during installation may result in breakage. Mirrors 4 and 6 are attached to the mirror table components 4a and 6a, respectively, with two-sided adhesive tape. The two-sided adhesive tape is placed on the reverse side of the mirrors 4 and 6 at appropriate intervals, and is adhered to the mirror table components 4a and 6a. Empty spaces are formed between the back surface of the mirrors 4 and 6 and the mirror table components 4a and 6a where there is no two-sided adhesive tape applied. Carelessly pressing on these areas may result in breakage of the mirrors 4 and 6.
The mirrors 4 and 6 have a length that is longer than their width, which may prevent light rays from striking the mirrors unless they are adequately extended in a predetermined direction. In addition, because of the use of two-sided adhesive tape, the mirror is easily shifted in position. Peeling-off the adhesive tape to correct for the shift may also result in breakage of the mirrors 4 and 6.
After attachment, the mirrors 4 and 6 must be inspected to assure that the mirror is facing in the predetermined direction, but because the mirrors 4 and 6 are narrow, it is difficult to inspect the entire mirrors 4 and 6 prior to and during installation. This makes mass production difficult. Inspection is performed by obtaining chart image data that is available only after the product has been assembled. Discovery of defective products at this point results in a lower yield of acceptable products.